---
title: Dynamic code evaluation is not available in Middleware
---

## Why This Error Occurred

`eval()`, `new Function()` or compiling WASM binaries dynamically is not allowed in Middleware.
Specifically, the following APIs are not supported:

- `eval()`
- `new Function()`
- `WebAssembly.compile`
- `WebAssembly.instantiate` with [a buffer parameter](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiate#primary_overload_%E2%80%94_taking_wasm_binary_code)

## Possible Ways to Fix It

You can bundle your WASM binaries using `import`:

```ts filename="middleware.ts"
import { NextResponse } from 'next/server'
import squareWasm from './square.wasm?module'

export default async function middleware() {
  const m = await WebAssembly.instantiate(squareWasm)
  const answer = m.exports.square(9)

  const response = NextResponse.next()
  response.headers.set('x-square', answer.toString())
  return response
}
```

In rare cases, your code could contain (or import) some dynamic code evaluation statements which _can not be reached at runtime_ and which can not be removed by tree-shaking.
You can relax the check to allow specific files with your Middleware [configuration](/docs/pages/api-reference/edge#unsupported-apis):

```tsx filename="pages/api/example.ts"
export const config = {
  unstable_allowDynamic: [
    '/lib/utilities.js', // allows a single file
    '/node_modules/function-bind/**', // use a glob to allow anything in the function-bind 3rd party module
  ],
}
```

`unstable_allowDynamic` is a glob, or an array of globs, ignoring dynamic code evaluation for specific files. The globs are relative to your application root folder.

Be warned that if these statements are executed on the Edge, _they will throw and cause a runtime error_.
